curiousmarc
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HP 9500A Rack Taking Shape
🕑 Added 2021-03-07 03:38:56 +0000 UTCI hauled back an original HP rack from LA during my latest trip, from Ed Blacksmith. I bought it specifically to hold my HP test instruments from the 1960s. This is meant to be the second rack of an HP 9500A Automated Test System, like this one in the 1968 Catalog:
In the catalog picture, the rack on the left is an HP 2116, HP's first computer, a 16 bit machine with 16k of core memory. You probably have spotted it in the background of my videos, the rack to the left of my "Teletype Shop" sign.
Here is the other side of the beast, showing the wire-wrapped backplane and the double core stack hanging at the back of it, and a piece of Carl behind the rack.
The other rack would hold all the instruments, usually Nixie instruments, from which the computer reads the data in BCD - this is way before HP-IB. Also generators such as computer controlled power supplies and frequency generators. So I put all my HP Nixie stuff in there plus most of my other 1960's instruments for good measure.
This test equipment rack will complete my new old 9500 system, which was fully customizable with whatever instruments you wanted. From top to bottom, an HP 180D scope (donated by Robert Garner, who also donated the HP 2116B!), an HP 2402 voltmeter (donation from Bob Rosenbloom), which was the core instrument of the HP 9500A system, a magnificent and even older HP 3460B voltmeter donated by viewer Jim Gallagher, also picked up during the recent LA haul. Then the HP 7035B Chart Recorder brought back from the same trip from the Max Sands auction. Then two Nixie counters, the classic HP 5245L frequency meter, with a 500 MHz converter plug-in in the right drawer. That's another Bob Rosenbloom unit that got to someone else first but was unused, so it came back to me. It sure does not work (yet!). I got all of the 3 other plug in converter drawers from the Max Sands auction, which extend the frequency meter to 4 GHz! Then an HP 5223L 300 kHz frequency meter/counter, found at a swap meet. And finally an HP 6130B, HP's first programmable +/-50V power supply. That one is from eBay. I also finally got the +/-100V HP 6131C that was languishing for years at Excess Solutions, when I was there for my Apollo box. It's not yet in the rack.
At the very bottom, there would be a crossbar switch (from a telephone switch) or a relay scanner, so the inputs and outputs could be multiplexed to the few digital meters and digital supplies. But I can't find any, so I put a random patch panel in there for the moment. If you guys have a crossbar laying around...
It takes a ton of work to rack these, as every single instrument needs two custom rails to be build: they are far too heavy to just hang from the front. I also had to machine a couple of side ear brackets when the instruments did not have them. These 1960s brackets are different from the later brackets, and not easily found on eBay. Lots of cutting and drilling angle aluminum.
So far, the only instruments that seem to fully work are the 2402 voltmeter, the 5223 freq meter, the 6130 supply and the 7035 chart recorder. The 2402, 5223 and 6130 worked right off the bat, just needed inspection and cleaning! The 7035 chart recorder, I couldn't wait, and restored it in less than two days off camera just after I brought it back.
But that does not prevent me to turn on the whole thing, dim the lights, and admire the warm Nixie glow, as luckily they all light up!
Marc
Comments
Nathan Davey
We still have a couple racks like that at work, no one really know how use them, in there entirety anymore, though
CuriousMarc
Very true. I was lucky that I had a couple examples I could measure and reproduce.
As someone more often working the mechanical side of these things, I've always found it remarkable (and frustrating) how poorly-documented things like these rack ears and rails so often are. Even if you can find a reference to what part number they were supposed to be, they're so easy to get misplaced from the equipment they're matched to, and then lost in a pile of awkward scrap-metal.
